OBJECTIVE: To characterize the cholesterol feedback control of beta-hydroxy-beta-methylglutaryl CoA reductase in tissue culture of normal and malignant liver cells. APPROACH: Primary rat liver cell cultures and cultures of hepatoma cells will be assayed for beta-hydroxy-beta-methylglutaryl CoA (HMG CoA) reductase. The rate of derepression of this enzyme in the two types of cells will be determined by growing each cell type in cholesterol-free media; and the influence of actinomycin D and of cycloheximide upon the derepression of this enzyme will be examined. Finally lipoprotein fractions from both cholesterol fed rabbits and hypercholesterolemic human beings will be added to the culture media to determine the ability of such lipoproteins to inhibit HMG CoA reductase.